1. Field of the Invention
This invention relates in general to a thin film magnetic head and, more particularly, to an improved pole tip structure for a thin film magnetic head.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to as a thin film magnetic head, and this transducer has met the requirements for magnetic recording technology for many years. In magnetic recording technology it is continually desired to improve the areal density at which information can be recorded and reliably read. For this reason, the design of thin film magnetic heads has changed to meet the changing density requirements.
For example, a prior art design is shown in FIG. 2 in which the width of the first pole piece P1 deposited on the substrate was greater than that of the second pole piece P2 to prevent a problem associated with misregistration between the pole pieces. Tighter side reading and side writing specifications lead to the trimmed pole tips shown in FIG. 3. In this case, the width of the pole tips was not limited to the precision with which the pole tips could be deposited, since the pole tips were trimmed by ion milling, for example, to a specified width with both pole tips P1 and P2 substantially the same width. However, since conventional ion milling processes generally require a thick photoresist process, the method is limited for narrow track width applications where a very high aspect ratio of resist height to width is required.
There has been some attempt to improve the performance of thin film magnetic heads by the use of a composite magnetic structure. For example, the publication IBM Technical Disclosure Bulletin, Vol. 15, No. 7, December, 1972, p. 2182, describes a magnetic head in which the magnetic circuit is formed of upper and lower ferrite blocks 2 and 8, a permalloy back gap closure 5, and permalloy pole pieces 4 and 10 which contact the ferrite blocks and extend to the air bearing surface.
U.S. Pat. No. 4,589,042 discloses a thin film inductive head in which both the upper and lower pole pieces are deposited in two steps. In one step the yoke is produced, and in the subsequent step the pole tip is produced so that the yokes and pole tips can be produced of different magnetic materials.
U.S. Pat. 4,839,197 discloses a thin film inductive head in which the lower magnetic pole is produced in whole and the upper magnetic pole is produced in parts. The first part is the pole tip region after which the coil is produced, and the remainder of the upper magnetic pole is then produced in contact with the pole tip region and with the back gap region.
None of the references disclose a thin film magnetic head in which the pole tips and gap layer are produced separately and are in contact with the magnetic yoke layers at the air bearing surface so that precisely formed thick pole tips can be produced.